• Volume 4, Issue 4

      July 1982,   pages  375-481

    • Amorphous semiconductors: Structural models

      J Nag S P Sen Gupta

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      The structure of amorphous semiconductors has become the subject of intense study in recent years. In this paper, the models, that have been constructed and applied to represent the structures, have been briefly reviewed. Details of the construction of continuous random network (CRN) models have been presented and a comparative study of the microcrystallite model and the random network model has been made in the light of their recent applications.

    • Defects in GaAs

      V Swaminathan

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      A comprehensive review of defects in GaAs with focus on native point defects and dislocations is given. The effects of these defects on devices are also considered. It is pointed out that a unified point defect model cannot at present be drawn from the available information. The importance of including anti-site defects in the point defect models which have hitherto only considered vacancies and interstitials is stressed. Attention is drawn to the need for understanding the dominant equilibrium native defects in GaAs both from fundamental and technological considerations. In this respect new experimental techniques are suggested to understand and control the defect structure. The current understanding of dislocations in GaAs is very much in its infancy compared to that in elemental semiconductors. Both theoretical work and careful experiments are wanting. This is essential since dislocations have been directly implicated in the degradation of GaAs devices.

    • X-ray topographic analysis of dislocation line defectsin calcium fluoride crystals

      C C Desai

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      One-to-one correspondence of dislocation etch pits have been established on the matched cleavage faces and on the opposite sides of thin flakes of calcium fluoride crystals. By selecting 022 and 022 reflections and MoKα1 radiation, stereopair projection x-rays topographs were studied and critically compared with optical micrographs. The dislocation etch pits and dislocation out crop images show a close resemblance. The orientation of the Burgers vectors of the dislocation lines has been identified and these lines lie parallel to the <110> directions. The growth history of the stratigraphical pattern has been studied using x-ray topographic technique.

    • Structural, magnetic and electrical study of CoMnAlO4

      S G Joshi D K Kulkarni P V Khandekar

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      A spinel CoMnAlO4 has been synthesised by the oxide method. It has a tetragonal structure withA=8.10 A andC=8.22 A. A break is found in the plot of logρ against 1/T at 573°K when activation energy changes from 0.62 eV to 0·52 eV. The electrical properties show that it can be regarded as a properly substituted CoMn2O4 by Al+3 ions. It is paramagnetic withCM = 4.72 and ϑa= −298°K. These results show the ionic configuration of the compound as Co+2 [Mn+3 Al+3]O4.

    • High temperature resistivity characteristics of nonstoichiometric V2O3

      H Jhans J M Honig

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      The resistivity anomaly encountered in stoichiometric V2O3 is gradually suppressed with increasing density of cation vacancies. These observations are discussed in terms of related findings reported in the literature.

    • Optical constants of MoxW1−xSe2 single crystal solid solutions

      M K Agarwal P D Patel O Vijayan

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      Single crystal solid solutions in the series MoxW1−xSe2 (0≤x≤1) have been studied by reflectivity measurements at oblique angles of incidence. The optical constants at a few wavelengths have been determined.

    • A note on the composition dependence of elastic properties of Se-P glasses

      V C Padaki S T Lakshmikumar A M Jayannavar E S R Gopal

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      Longitudinal and shear wave ultrasonic velocities are reported in Se-P glasses over the composition range 0–50 at % P. The glass transition temperaturesTg show maxima at 30 and 50 at % of P, in consonance with earlier data. The bulk modulus shows minima at these compositions, contrary to the expectation of maxima. These are discussed in relation to the formation of compounds at specific compositions and the nature of the covalent bonding in the glasses.

    • Microstructures, thermal diffusion and decomposition studies in the two phase solution grown mixed crystals of NaCl and KCl

      S R Ghadekar B T Deshmukh

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      Mixed NaCl-KCl crystals are grown from water solution. Thermal diffusion, decomposition and microstructures studies by employing the etching technique are reported. It is shown that microstructures consisting of alternate lamellae of NaCl and KCl arranged in 〈100〉 and 〈110〉 directions in the two-phase mixed NaCl-KCl crystals observed at room temperature get converted to the one consisting of random mixture of both the phases on finer scale on heating at 300°C for 30 hr. The dissociated matrix on heating at 600°C for 15 hr regains almost all the characteristics of a single crystal transforming the material into single-phase mixed (NaK) Cl crystals. The temperature dependence of the thermal diffusion is discussed.

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